Modern internal combustion engines are typically fed fuel from a fuel tank system. The fuel tank system usually includes an evaporative emission control system (“EVAP system”) that collects fuel vapors generated by fuel in the fuel tank system. These fuel vapors, among other things, pose an environmental and safety hazard. A typical EVAP system includes a canister connected to the fuel tank that collects and stores fuel vapors emitted from the fuel tank. A purge valve is usually located between an intake manifold of the engine and the canister. It is desirable to check the EVAP system to ensure that it does not contain any leaks. An electronic controller controls the components of the typical EVAP system to determine whether a leak is present. A typical test method, as disclosed in U.S. Pat. No. 6,314,797, creates a vacuum in the EVAP system and monitors the system pressure to determine whether a leak is occurring.
Many engines in modern automobiles are fed compressed air by a turbocharger, supercharger, or some other device. These forced induction engines usually include vacuum ejector tee hardware in the EVAP system. The vacuum ejector tee typically includes integrated check valves to prevent the backflow of air from the forced induction engine into the evaporative system. However, the addition of the vacuum ejector tee prevents the proper vacuum from forming in the fuel tank system for the EVAP system test.
What is needed, therefore, is a method for testing the EVAP system in a forced induction engine.